Bypass Catalyst Diagnostic System for Rapid Light-Off
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Solution Overview
Problem
Conventional engine exhaust aftertreatment systems face challenges in achieving low tailpipe emissions immediately after a cold engine start due to low catalyst conversion efficiency, which is often addressed by increasing light-off temperatures at the cost of backpressure, durability, longevity, and complexity.
Innovation Solution
A light-off catalyst bypass system with a bypass catalytic converter and valve that directs exhaust gas through a bypass catalyst before the main exhaust path, allowing rapid catalyst light-off and improved conversion of harmful constituents, along with a diagnostic method using oxygen sensors to monitor and ensure the bypass catalyst's efficiency and functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the catalyst light-off temperature is increased to achieve low tailpipe emissions immediately after cold start, then emissions conversion efficiency is improved, but exhaust system backpressure increases and durability decreases
Solution Approach 1:
The exhaust aftertreatment system is segmented into two separate catalytic converters: a light-off catalyst positioned close to the engine for rapid warm-up and cold start emissions control, and a main catalyst positioned downstream for sustained emissions conversion. This segmentation allows each catalyst to be optimized for its specific function, with the light-off catalyst achieving fast light-off without compromising the main catalyst's durability and performance.
2Productivity
If a light-off catalyst bypass system is implemented to achieve fast catalyst light-off, then cold start emissions are reduced, but device complexity increases
Solution Approach 1:
A bypass valve serves as an intermediary component that selectively directs exhaust flow between the light-off catalyst and the main catalyst based on engine operating conditions. During cold start, the bypass valve routes exhaust through the light-off catalyst for rapid emissions control; during normal operation, it directs exhaust through the main catalyst. This intermediary mechanism enables fast cold start emissions conversion while maintaining system manageability through a single control component.
3Productivity
If the main catalyst is used for cold start emissions control, then emissions are reduced, but the main catalyst degrades faster and useful life is reduced
Solution Approach 1:
The system segments the emissions control function between two catalysts, protecting the main catalyst from the harsh thermal and chemical conditions of cold start operation. The light-off catalyst, positioned in the high-temperature zone near the engine, absorbs the thermal stress and rapid temperature cycling during cold start, while the main catalyst operates under more stable conditions, extending its useful life and maintaining performance over time.
4Speed
If a bypass system with high-cell-density catalyst is used, then light-off time is reduced, but manufacturing cost increases
Solution Approach 1:
The system uses a high-cell-density light-off catalyst in a segmented configuration positioned close to the engine, where it only needs to handle cold start emissions. This allows the use of expensive high-performance catalyst material only where it is most needed for rapid light-off, rather than throughout the entire exhaust system. The main catalyst can use more cost-effective materials since it operates under more stable conditions, achieving cost optimization through functional segmentation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves extremely fast catalyst light-off times, high conversion efficiency, and reduced degradation of the main catalyst by selectively using a high-cell-density bypass catalyst, while maintaining emissions compliance and extending the useful life of the catalyst.
Implementation Method 1
a bypass catalytic converter configured to selectively receive exhaust gas from the internal combustion engine
Implementation Method 2
A controller in signal communication with a first oxygen sensor disposed upstream of the bypass catalytic converter, and a second oxygen sensor disposed downstream of the bypass catalytic converter
Implementation Method 3
when the bypass valve is in the first position, the turbine is operated in a reverse rotation to facilitate preventing the exhaust gas from passing through the turbine
Data Source
AI summary
An engine system includes an internal combustion engine, a main exhaust aftertreatment system with a main catalytic converter, and a light-off catalyst bypass system with a bypass catalytic converter. An emissions control system includes a controller in signal communication with a first oxygen sensor disposed upstream of the bypass catalytic converter, and a second oxygen sensor disposed downstream of the bypass catalytic converter. The emissions control system performs a diagnostic of the bypass catalytic converter, including (i) monitoring signals from the first and second oxygen sensors for a predetermined time period during an engine cold start condition, (ii) determining a signal average of the first oxygen sensor (iii) determining a signal average of the second oxygen sensor, (iv) determining a difference between the signal averages of the first and second oxygen sensors, and (v) comparing the difference to a predetermined threshold to determine if the bypass catalytic converter has failed.